Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 13896)
+++ wp-includes/pluggable.php	(working copy)
@@ -447,9 +447,10 @@
 
 	$phpmailer->ContentType = $content_type;
 
-	// Set whether it's plaintext, depending on $content_type
+	// Check if we're dealing with an HTML email
+	// MsgHTML marks email as HTML and creates plain text copy, albeit a terrible one
 	if ( 'text/html' == $content_type )
-		$phpmailer->IsHTML( true );
+		$phpmailer->MsgHTML( $message );
 
 	// If we don't have a charset from the input headers
 	if ( !isset( $charset ) )